The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear one and one-half (1½) times as well on the government course as a tire graded 100.
The relative performance of tires depends upon the actual conditions of their use, however, and may depart significantly from the norm due to variations in driving habits, service practices and differences in road characteristics and climate.
The vehicle should be checked by a retailer/authorized repairer as soon as possible if treadwear is uneven across the tire, or a tire wears excessively.
When the tread has worn down to approximately 0.07 in (2 mm), wear indicators start to appear at the surface of the tread pattern. Wear indicators produce a continuous band of rubber across the tread, as a visual indicator.
Wear indicators show the minimum tread depth recommended by the manufacturers. Tires which have worn to this point will have reduced grip and poor water displacement characteristics. Worn tires can lead to accidents, with the potential to cause serious injury or death.
Local legislation may determine a greater minimum tread depth to that shown by the tire wear indicators. Making sure that the tread depth meets the local legal requirements remains the responsibility of the driver. Do not rely on the tread depth indicators alone.